Rheostat voltage compensator for ignition systems



Jan. 22, 1963 G. E. MICHAUD 3,075,029

RHEOSTAT VOLTAGE COMPENSATOR FOR IGNITION SYSTEMS Filed Jan. 13, 1961 RY V 9 OLT IO Fl 2 2O G fie: D m

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INVENTOR. GEORGE E. MICHAUD A TDB NE I mm 4 United States Patent C) 3,ti75,ti29 RHEOSTAT VQLTAGE COMPENSATOR FOR IGNHTEQN SYSTEMS George E. Michaud, 36 Buchanan Road, Salem, Mass. Filed Jan. 13, 1961, Ser. No. 82,479 9 Claims. (Cl. 123-148) This invention relates to ignition systems, and more particularly to ignition systems of the battery-energized type for internal combustion engines.

In a conventional automobile ignition system, the voltage available at the spark plugs decreases with increasing engine speed, because the decreasing interval of cont-act of the interrupter contacts of the distributor does not permit maximum voltage to be built up in the spark coil. However, the voltage required for proper ignition does not decrease appreciably with increasing speed; and acceleration requires a sharp rise in ignition voltage, be cause of the accompanying increase in pressure in the compression chamber. Misfiring occurs when the voltage requirement is in excess of that available, and may occur even with new spark plugs in an automobile driven at high speeds or with rapid acceleration. As the spark plug electrodes become worn or the insulators coated with deposits, however, their voltage requirement increases sharply, and misfiring occurs even under moderate speeds and accelerations. While this misfiring may not be notice-able to the operator, it results in a decline in power and efficiency which makes frequent replacement of the spark plugs desirable, although expensive.

This problem cannot be satisfactorily resolved merely by increasing the voltage supplied to the spark plugs by the coil. The high voltage applied to the tungsten interrupter contacts of the distributor causes arcing as they break, and the resulting high temperature in the arc, which may reach 9,0 F. in practice, eventually causes the contacts to become eroded. The rate of erosion depends upon the applied voltage. Similarly, erosion of the spark plug electrodes occurs more rapidly as the applied voltage is increased. The temperature at the gap of the electrodes may momentarily reach 27,000 F. when they are subjected to the maximum voltage available in actual practice.. Any increase in voltage above that required for efficient ignition consequently results only in more rapid wear of the interrupter contacts and spark plug electrodes. In order to reduce wear of the contacts and spark plugs, it is a conventional practice to provide 12 volt ignition systems with a fixed resistor to limit the primary ignition voltage to 9 volts. However, this limitation of voltage results in misiiring at an early stage of wear of the spark plugs, under accelerating or high speed conditions, and requires their frequent replacement.

It is the primary object of my invention to provide an improved ignition system having means for increasing the useful life of spark plugs.

It is another object of my invention to provide an improved ignition system having means for preventing misfiring without increasing the rate of wear of spark plug electrodes and interrupter contacts.

It is still another object of my invention to control the voltage supplied to the spark plugs of an ignition system in accordance with the voltage demanded for efiicient ignition under various operating conditions.

Further objects and advantages of the invention will become apparent as the following description proceeds.

Briefly stated, I may carry out my invention by inserting a variable resistance element, or rheostat, in series relation in a conventional ignition circuit, and by providing means for controlling the resistance of the rheostat in accordance with the ignition voltage requirement of the engine. These means are arranged to vary the resistice ance as an inverse function of the throttle valve opening, which I have found to be a practical measure of the voltage requirement. Either the throttle position or the manifold pressure may be employed for this purpose.

By these means, the voltage applied to the spark plugs is controlled to maintain values which are sufficient to afford eflicient ignition under all operating conditions, but which are not so much in excess of ignition requirements as to cause unnecessarily rapid wear of the interrupter points and spark plug electrodes.

I further provide means for adjusting the rheostat to obtain a variation in the relationship between the resistance and the control function. By these means, the rheostat may be adjusted to decrease the level of resistance with respect to the control function as the spark plugs become worn, thus increasing the level of the ignition voltage to maintain efficient ignition and provide an extended useful spark plug life. When new plugs are installed, the rheostat is adjusted to increase the level of resistance to values such that while efiicient ignition is continued, the secondary voltage is not so much in excess of the required ignition voltage as to cause erosion of the interrupter contacts and the spark plug electrodes at an unnecessarily rapid rate.

According to a preferred embodiment of the invention, I provide a rheostat having a rotatable control arm, and drivingly connect the arm with a conventional throttle linkage so that the resistance placed in the circuit of the primary coil is decreased as the throttle is opened by the foot of an operator depressing the accelerator pedal. In this manner, the resistance is controlled in inverse relation to the throttle opening, and is decreased during acceleration of the automobile, as well as during high speed operation. The resistance value of the rheostat is selected to maintain a secondary voltage somewhat in excess of that required throughout the entire speed range of the engine. I also provide an adjustable driving connection between the control arm of the rheostat and the throttle linkage, so that the rate of movement of the arm relative to the throttle lever may be adjusted to conform closely to the voltage requirement.

In another embodiment of the invention, the rheostat arm is drivingly connected to a spring-loaded diaphragm which is arranged to be actuated by the pressure obtaining in the engine manifold. This pressure is less than atmospheric pressure, and is therefore conventionally referred to as vacuum. The pressure increases sharply low vacuum during acceleration or at high speed and decreases high vacuum at low speeds and during deceleration. The diaphragm is arranged to rotate the arm in a direction to decrease the resistance of the circuit when the engine is accelerated or operated at high speed, thus obtaining a similar result to that achieved by the first embodiment.

While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which I regard as my invention, it is believed that the invention will be more clearly understood from the following detailed description of a preferred embodiment thereof, referring to the accompanying drawing, in which:

FIG. 1 is a schematic representation of an ignition system according to a preferred embodiment of the invention;

FIG. 2 is a diagram comparing the secondary voltage made available to spark plugs by a conventional ignition system with that atforded by the improved system; and

FIG. 3 is a schematic representation of another embodiment of the invention.

Referring to FIG. 1, a preferred embodiment of the invention is shown in combination with the elements of a conventional ignition system. The system includes a battery 1, anignition switch 2, spark coil 3, a distributor 4, and a plurality of spark plugs, one of which is shown at 5. The ignition switch includes conventional starting and ignition terminals, as designated in the drawing, for energizing a conventional starting motor (not shown) in the starting position, and for de-ene'rgiz'ing the starting motor when an associated engine (not shown) is in self-sustaining operation.

The negative terminal of the battery is grounded, while in the star'ting position of the ignition switch, the positive terminal is connected in series relation with a primary coil of the spark coil 3 through a conductor-6am a trf minal 7. The primary and secondary coils are connected intermittently to a common ground by meansof a ter minal 8, a conductor 9, a terminal 10, and by an interrupter (not shown) of the distributor 4, which is connected inpa'rallel witha condenser 11. The secondary coil isconnected with a distri-butorarm (not shown) through a conductor 12. The spark plugs receive ignition voltage from the distributor through a plurality of con ductors, one of which is shown at 13' connected to the spark plug 5. The ignition system thus far described is well-known in the art, and no further detailed description is believed necessary. I prefer to connect the battery directly to the primary terminal 7 without intervening resistance during starting, in order to provide a maximum starting voltage.

According to customary practice, a fixed resistor would be inserted in series between the battery and the primary coil in the ignition position of the switch,- so as to limit the secondary voltage to values just suificient to fire relatively new spark plugs under high speeds and accelerations, and thus somewhat reduce the rate of wear of the spark plug electrodes and interrupter contacts. However, the use of a fixed resistance also results in misfiring of the spark plugs after a relatively brief period of use, as their voltage requirement rises. In FIG. 2, the relationship between automobile speed and available secondary voltage is graphically depicted. The ignition voltage available in aconventional system, shown in curve A, decreases uniformly with increasing speed, because of the reduction in the interval of engagement of the interrupter con tacts. The voltage available is greatly in excessof that required to'fire the plugs under the high cylinder pressures associated with low speeds, but is barely sufiicient for acceleration and for high-speed operation. The'fixed resistance of the system requires that an excessive voltage be supplied at low speeds, thus causing unnecessarily rapid wear of the spark plugs. Furthermore, the voltage requirement rises as the plug electrodes become eroded with wear, and the system may not be capable of satisfying this requirement under conditions of acceleration or at high speed, when cylinder pressure is high, so that misfiring results.

According to the invention, I provide means for controlling the ignition voltage in accordance with engine requirements. Referring again to FIG. 1, these means include a rheostat 14 having a resistance wire 15 helically wound upon an arcuateinsulator core 15a. The rheostat is provided with mounting tabs 14a, having elongated fastener-receiving slots 14b for convenient adjustment of the range of resistance afforded by the rheostat, according to the state of wear of the spark plugs. One end of the resistance wire 15 is connected to the conductor 6 by means of an extended terminal 16 and a conductor 17. A control arm or element 18 is rotatably mounted upon the rheostat by means of a clevis pin 19 and a cotter pin 20. An alternative opening 21 for the clevis pin permits the radius of the arm 18, and thus its arcuate range of movement, to be adjusted. The arm carries a contac't 22: which is suitably insulated therefrom and connected to the ignition terminal of the switch 2 by means of a condoctor 23. The contact is movable along the resistance wire'15by rotation of the control arm toinsert a variable resistancein series relation between the battery and the primary coil when the switch is in-the ignition posi- 49 tion. The extended terminal 16 permits extended clockwise movement of the control arm without further variation in resistance.

The control arm 18 is drivingly connected at its lower end with a throttle linkage including pivotally connected levers 24 and 25, by means of a clevis pin 26 and a cotter pin 27. An alternate opening 28 is formed in the arm to-receive the clevis pin, for adjustment of the rate of movement of the arm with respect to the throttle linkage.

In a conventional manner, one end of the throttle lever 24 is secured to a foot-operated accelerator pedal 29, which is mounted in an interior surface 29a of the automobile. At its opposite end, the throttle linkage is connected by means of a bell crank 30 and levers 31 and 32 to the throttle valve 33 of a carburetor 34. Depression of the pedal 29 to accelerate the engine or to maintain a relatively high speed causes the arm 18 to rotate in a clockwise direction, decreasing the resistance of the circuit in inverse relation to the throttle valve opening.

A diagram of the available voltages in the improved system of FIG. 1 is shown in curve B in FIG. 2. The voltage available remains in excess of that actually required for ignition at all constant speeds, but is limited to values which are not so large as to cause erosion of the electrodes and interrupter points at an unnecessarily rapid rate. It should be noted that the voltage required at constant speeds may be quite low; for example, only 5000 volts may be required at a steady speed of 30 m.p.h. on a level road. Acceleration initially increases cylinder pressure, however, and sharply increases the voltage requirement. In my improved system, opening of the throttle quickly reduces the resistance of the circuit to increase the available voltage. This action is illustrated by curves C and D, showing the voltage made available by the system upon typical accelerations from 30 and 60 mph, respectively. In this manner, the throttle opening serves as an efficient function for controlling the ignition circuit resistance in accordance with ignition voltage requirements.

An alternative embodiment of the invention is shown in FIG. 3. In this modification, a variable resistor or' rheostat 40 is arranged to be controlled by the pressure obtaining in an intake manifold 41 of an associated internal combustion engine. The rheostat includes a resistance wire 43 wound helically about an arcuate insulator 42 and connected to an extended conducting terminal 44, which serves to permit extended travel of a control arm or element 45 without further variation of resistance. A terminal screw 46 secures a conductor 47 in conductive relation to the terminal. A conductor 48 is connected to a contact 49, which is mounted upon the arm 45 and suitably insulated therefrom, for slidably engaging the resistance wire 43. The conductors 47 and 48 connect the resistance wire in series between a spark coil and a battery or other voltage source (not shown), as m the embodiment of FIG. 1. The arm 45 is pivotally mounted on the rheostat 4%} by means of a clevis pin 50 and a cotter pin 51. The rheostat is provided with mounting tabs 54 and 55, which are formed with elongated mounting slots 56 and 57, respectively, to permit manual ad uStment of the relative position of the resistance element 43 with respect to the arm 45. The level of resistance corresponding to various levels of manifold pressure may thus be adjusted to accommodate both old and new spark plugs, in a manner similar to that previously describcdin the embodiment of FIG. 1.

A throttle lever 59 is secured by means of a clevis pin 60 and a link 61 to the throttle valve 63 of a carburetor 64, and the carburetor is mounted upon the intake manifold 41 in a conventional manner. The degree of vacuum obtaining in the intake manifold varies in inverse response to the acceleration and speed of the engine, and to the throttle opening. I utilize the vacuum as a controlfunction to modulate the resistance of the ignition circuit by providing a diaphragm 7t) drivingly connected with the control arm 45 by means of a link 71. The link is secured to the control arm by means of a clevis pin 72 and a cotter pin 73, and is cemented to the diaphragm or secured thereto in any other suitable manner. The diaphragm is peripherally sealed within a casing 74 to form an air-tight chamber 75 and a chamber 76 which is open to the atmosphere through an opening 77 formed in the casing. A compression spring 78 is disposed in a cylindrical portion 79 of the casing to urge the diaphragm and the link toward the right as viewed in FIG. 3. A conduit 811 communicates with the manifold 41 and with the chamber 75 through conventional air-tight fittings 81 and 82, respectively. The manifold pressure is thus applied to the diaphragm 70, in opposition to the atmospheric pressure in the chamber 76. The manifold pressure, which is normally less than atmospheric, permits the atmospheric pressure to urge the lever 71 and the arm 45 toward the left as viewed in FIG. 3, against the bias of the spring 78.

By these means, the position of the control arm 45 and the ignition circuit resistance are regulated in direct response to the degree of manifold vacuum, which is an inverse function of the speed and acceleration of the engine, and of the throttle opening. I have found that the manifold vacuum is an adequate control function; however, I prefer to utilize throttle opening directly as the control function, as in the embodiment of FIG. ll, because of the greater sensitivity of the latter with respect to ignition voltage requirements.

While I have shown and described preferred embodiments of my invention for purposes of illustration, it will be apparent to those skilled in the art that various changes and modifications may be made Without departing from the spirit and scope of the invention. I therefore intend to cover all such changes and modifications in the appended claims.

What I claim and desire to secure the United States is:

1. Apparatus adapted for controlling the ignition voltage supplied by means of an ignition circuit to a spark plug of an internal combustion engine having a throttle valve, said apparatus comprising, in combination: a rheostat in electrical series relation in said ignition circuit, said rheostat having a movable control element for varying the resistance thereof, and means drivingly connected with said control element for controlling the resistance of said rheostat as a continuous inverse function of the opening of the throttle valve of the engine independently of the engine speed.

2. For use in an internal combustion engine having a throttle valve, an ignition circuit and a spark plug for the ignition of fuel; the combination with said ignition circuit of a rheostat interposed in electrical series relation therein, a movable control element for varying the resistance of said rheostat, and means responsive to the opening of the throttle valve, said means drivingly connected with said control element to vary the resistance of said ignition circuit in inverse relation to the opening of the throttle valve, independently of the engine speed.

3. The combination recited in claim 2, in which the driving connection between said control element and said means is adjustable to provide an adjustable relationship between the resistance of said ignition circuit and the opening of the throttle valve.

4. In an internal combustion engine having a throttle valve movable between open and closed positions for controlling the speed and acceleration of the engine, a throttle lever manually movable to control the opening of said throttle valve, and an ignition circuit including a spark plug for ignition of fuel, the combination therewith of a rheostat interposed in electrical series relation in said ignition circuit, and a movable control element for varying the resistance of said rheostat, said throttle lever beby Letters Patent of ing drivingly connected with said control element to vary the resistance of said ignition circuit in inverse relation to the opening of said throttle valve, independently of the engine speed.

5. The combination recited in claim 4, in which said throttle lever is adjustably connected with said control element for adjustment of the relationship between the resistance of said ignition circuit and the opening 'of said throttle valve.

6. In an internal combustion engine having a throttle valve movable between open and closed positions for controlling the speed and acceleration of the engine, a throttle lever manually movable to control the opening of said throttle valve, and an ignition circuit including a source of voltage, a spark coil, and a spark plug arranged in series relation for ignition of fuel; the combination therewith of an elongated resistance element, a control element, and a contact carried by said control element in slidable engagement with said resistance element, said contact and said resistance element being interposed in electrical series relation between said source of voltage and said coil, said control element being rotatably supported for varying the resistance of said ignition circuit, said throttle lever being drivingly connected with said control element to vary the resistance of said ignition circuit in inverse relation to the opening of said throttle valve, independently of the engine speed.

7. In an internal combustion engine having a fuel mixture intake manifold in which the pressure varies in relation to the speed and acceleration of the engine, and an ignition circuit including a spark plug for ignition of the fuel mixture; the combination therewith of a rheostat interposed in electrical series relation in said ignition circuit, a movable control element for varying the resistance of said rheostat, and pressure-responsive means in communication with said manifold and drivingly connected with said control element to vary the resistance of said circuit in inverse relation to the pressure in said intake manifold, independently of the engine speed.

8. The combination recited in claim 7, in which said pressure-responsive means is adjustably connected with said control element for adjustment of the relationship between the resistance of said ignition circuit and the pressure in said intake manifold.

9. In an internal combustion engine having a throttle valve movable between open and closed positions for controlling the speed and acceleration of the engine, a fuel mixture intake manifold in which the pressure varies in relation to the opening of the throttle valve, and an ignition circuit including a source of voltage, a spark coil, and a spark plug arranged in series relation for ignition of fuel; the combination therewith of an elongated resistance element, a control element, a contact carried by said control element in slidable engagement with said resistance element, said contact and said resistance element being interposed in electrical series relation between said source of voltage and said coil, said control element being rotatably supported for varying the resistance of said ignition circuit, and pressure-responsive means in communication with said manifold and drivingly connected with said control element to vary the resistance of said ignition circuit in inverse relation to the pressure in said intake manifold, independently of the engine speed.

References Cited in the file of this patent UNITED STATES PATENTS Re. 18,136 Fischer-Hinnen July 28, 1931 1,244,124 Paquit Oct. 23, 1917 1,549,732 Boughton Aug. 11, 1925 1,679,159 French July 31, 1928 1,752,445 Mallory Apr. 1, 1930 2,037,059 Beltz Apr. 14, 1936 

1. APPARATUS ADAPTED FOR CONTROLLING THE IGNITION VOLTAGE SUPPLIED BY MEANS OF AN IGNITION CIRCUIT TO A SPARK PLUG OF AN INTERNAL COMBUSTION ENGINE HAVING A THROTTLE VALVE, SAID APPARATUS COMPRISING, IN COMBINATION: A RHEOSTAT IN ELECTRICAL SERIES RELATION IN SAID IGNITION CIRCUIT, SAID RHEOSTAT HAVING A MOVABLE CONTROL ELEMENT FOR VARYING THE RESISTANCE THEREOF, AND MEANS DRIVINGLY CONNECTED WITH SAID CONTROL ELEMENT FOR CONTROLLING THE RESISTANCE OF SAID RHEOSTAT AS A CONTINUOUS INVERSE FUNCTION OF THE OPENING OF THE THROTTLE VALVE OF THE ENGINE INDEPENDENTLY OF THE ENGINE SPEED. 